GASTRODES I'ARASITICUM KORf^TNl'-KF. S7 



it sharp!}', not only from other members of the Platyctenea, but also 

 from those of all the remaining orders. Further, it may be pointed 

 out that, the occurrence of that stage in Gastrodes is an evidence for 

 the affinity of the two sub-divisions of the Coelenterata, Cnidaria and 

 Ctenophora, notwithstanding that certain authors are often inclined to 

 ignore the affinity and put greater emphasis on the relationship of the 

 Ctenophora with the Turbellaria. The planula of the present form, as 

 previously mentfoned, represents a solid mass of endoderm covered by a 

 skin of ectoderm. In this respect, and also in other structural features, 

 it resembles much the same stage of the Hydrozoa. This fact stands 

 possibly for the close relationship of the Ctenophora and the Hydrozoa. 

 The effect of the parasite to the host seems to be rather trifling, 

 and all the host showed normal development of the embryo, although 

 a contrary observation may be found in Heider's work ('93). 



Summary. 



(r). Gastrodes parasticnin Kokotneff is a parasitic ctenophore found 

 in the mantle of Salpa. 



(2). It shows some differences between individuals of different sizes 

 in its external and internal features. Lagest individuals measure about 

 3 mm. and smallest about o. i mm. in the diameter. of the body. 



(3). The structure of large individuals is essentially the same as 

 that of a cydippid. It is provided with an aboral sense-organ, eight 

 rows of comb-plates and a pair of tentacular apparatuses, each of the 

 same structure as that of a cydippid. The arrangement of the gastro- 

 vascular system is also the same as in that form. 



(4). Small individuals may be without the sense-organ, comb-plates 

 and tentacular apparatuses, moreover, the gastro-vascular system is more 

 or less simplified, as shown in PI. 8, figs. 3-8. 



(5). The most notable point concerning structure is that the 

 pharynx has been opened out to give the animal a flattened shape and 

 distinct dorsiventrality, the original external surface of the cydippid- 

 like body becoming the dorsal surface of the animal and the original 

 inner surface of the pharynx the ventral surface of it. 



(6). In the smallest individuals the shape of the body is cylindrical, 

 much as in cydippid ctenophores, and this stage is preceded by a 

 distinct planula stage showing ciliation on the whole external surface of 

 the body. The animal penetrates into the body of the host in this 



